When equipment such as a personal computer and the like are connected to networks such as a LAN, a phone network, and the like, it is necessary to protect the equipment from an ESD (Electrostatic Discharge) and a high voltage which intrude therein through a cable. To cope with the above problem, a pulse transformer is used for a connector constituting a connection point of the cable and the equipment.
A conventionally used pulse transformer is composed of a doughnut-shaped core (toroidal core) and a primary coil and a secondary coil wound around the core (refer to, for example, Japanese Patent Application Laid-Open No. 7-161535) and has a property for transmitting only the alternating component (pulses) of a voltage applied to the primary coil to the secondary coil. Since a direct current component is not transmitted to the secondary coil, the pulse transformer can shut off the ESD and the high voltage.
Recently, since it is also required to make a pulse transformer compact and surface mountable, examples that use a drum core in place of a toroidal core have been proposed. They are called a surface mount pulse transformer.
FIG. 15 shows a typical arrangement example of the surface mount pulse transformer. FIG. 16 is a view showing an equivalent circuit of the surface mount pulse transformer 1 shown in FIG. 15.
As shown in FIG. 15, the surface mount pulse transformer 1 has a drum type core 2 which includes a core 2a, around which wires are wound, and flanges 2b, 2c disposed on both the ends of the core 2a. Three terminal electrodes P1 to P3 and P4 to P6 are disposed on the upper surfaces of the flanges 2b, 2c, respectively.
As shown in FIGS. 15 and 16, wires S1 to S4 are wound around the core 2a, and both the ends S1a, S1b of the wire S1 are connected to the terminal electrodes P1, P2, both the ends S2a, S2b of the wire S2 are connected to the terminal electrodes P2, P3, both the ends S3a, S3b of the wire S3 are connected to the terminal electrodes P4, P5, and both the ends S4a, S4b of the wire S4 are connected to the terminal electrodes P5, P6, respectively.
The surface mount pulse transformer 1 is a circuit of a balanced input and output. As shown in FIG. 16, the terminal electrodes P1 and P3 act as a plus side terminal IN+ and a minus side terminal IN− of a balanced input, respectively. The terminal electrodes P4 and P6 act as a plus side terminal OUT+ and a minus side terminal OUT− of a balanced output, respectively. The respective wires are wound around the core 2a so that an induced current flows from the terminal OUT+ to the terminal OUT− when a current flows from the terminal IN+ to the terminal IN−. The terminal electrodes P2, P5 act as intermediate taps CT on an input side and an output side, respectively.
FIGS. 17A to 17H are views showing a winding process of the surface mount pulse transformer 1. As shown in FIGS. 17A to 17H, the winding process is divided into winding steps shown FIGS. 17A to 17D of a first layer and winding steps shown FIGS. 17E to 17H of a second layer.
The wires S1 and 54 are bifilar wound in the winding steps of the first layer. Specifically, the end S1a of the wire S1 is connected to the terminal electrode P1 first (FIG. 17A), and then the end S4a of the wire S4 is connected to the terminal electrode P5 (FIG. 17B). The wires S1 and S4 start to be wound together around the core 2a from one end side thereof counterclockwise when viewed from the one end side. When the wires S1 and S4 have been wound, the end S1b of the wire S1 is connected to the terminal electrode P2 (FIG. 17C), and then the end S4b of the wire 54 is connected to the terminal electrode P4 (FIG. 17D).
In the winding steps of the second layer, the wires S2 and S3 are bifilar wound. Note that the wires S1, S4 of the first layer are omitted in FIGS. 17E to 17H. Specifically, the end S3a of the wire S3 is connected to the terminal electrode P4 first (FIG. 17E), and then the end S2a of the wire S2 is connected to the terminal electrode P2 (FIG. 17F). The wires S2 and S3 start to be wound together around the core 2a from one end side thereof counterclockwise when viewed from the one end side. When the wires S2 and S3 have been wound, the end Sib of the wire S3 is connected to the terminal electrode P5 (FIG. 17G), and then the end S2b of the wire 2 is connected to the terminal electrode P3 (FIG. 17H).